1. Field of the Invention
This invention generally relates to a lock-up mechanism of a torque converter. More specifically, the present invention relates to a lock-up damper arranged in a lock-up mechanism for mechanically transmitting torque from a rotatable input body to a rotatable output body of a torque converter.
2. Background Information
In general, the damper mechanism reduces vibrations transmitted from the rotatable input body to the rotatable output body, while transmitting torque from the rotatable input body to the rotatable output body. One example of such a damper mechanism is a damper arranged in a lock-up mechanism of a torque converter (hereinafter referred to as a lock-up damper).
The torque converter is a device that has three types of runners (i.e., an impeller, a turbine and a stator) and normally transmits torque via hydraulic fluid. The impeller is secured to a front cover, which is connected to the rotatable input body. Torque of the impeller is transmitted to the turbine via hydraulic fluid flowing from the impeller to the turbine through the stator. The torque is then transmitted from the turbine to the rotatable output body, which is connected to the turbine.
The lock-up mechanism is typically arranged between the turbine and the front cover. The lock-up mechanism mechanically connects the front cover to the turbine under predetermined conditions in order to transmit torque from the rotatable input body to the rotatable output body.
Such a lock-up mechanism typically includes a piston, a drive plate and a driven plate. The piston is arranged to be urged against the front cover of the torque converter. The drive plate and a driven plate is secured to the piston. The coil springs are supported partially by the drive plate. The driven plate is elastically coupled in a rotational direction to the piston via the coil springs and drive plate. The driven plate is secured to the turbine, which is connected to the rotatable output body. The drive plate, the coil springs and the driven plate further constitute components of a lock-up damper that dampens transmitted vibrations in the lock-up mechanism.
As the lock-up mechanism is activated, the piston is urged against the front cover so that the piston is initially dragged along the front cover. As the piston positively frictionally engages the front cover, torque is transmitted from the front cover to the piston. The torque is then transmitted from the piston to the turbine through the coil springs of the lock-up damper. During this process, the lock-up mechanism not only transmits the torque but also dampens torsional vibrations by providing the lock-up mechanism with coil springs. The torsional vibrations are dampened as the coil springs are repeatedly compressed and expanded between the drive plate and the driven plate. When the coil springs are compressed and expanded, the coil springs slide along the drive plate, which is secured to the piston.
Since there is a strong market demand for downsizing of the torque converter, it is desirable to have a smaller lock-up mechanism. To meet this requirement, in many cases, the drive plate and the driven plate are arranged to oppose each other, and the coil springs are arranged in receiving windows formed in the drive plate and the driven plate. Specifically, the opposite ends of the coil springs engage the opposite circumferential end surfaces of the corresponding receiving window of the drive plate. Also the opposite circumferential end surfaces of the corresponding receiving window of the driven plate engage the opposite ends of the coil springs. Thus, the coil springs elastically couple the drive plate and the driven plate in a circumferential direction.
When the torque converter is rotated, a centrifugal force is applied to the components of the lock-up damper. In addition to the centrifugal force, the drive plate and the driven plate also receive the reaction forces applied from the coil springs in a circumferential direction. The drive plate and driven plate should have enough strength to prevent any damage to them when these centrifugal and circumferential forces are applied to the plates.
As described above, the drive plate and the driven plate should have enough strength to withstand the described forces. It is also desired to reduce the weight of the drive plate and the weight of the driven plate to reduce the weight of the torque converter. However, since these plates have the receiving windows for receiving the coil springs as described before, relatively high stresses are naturally occur around the receiving windows of the drive plate and the driven plate.
In view of the above, there exists a need for a lock-up damper which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.